‘Britain’s borders are sometimes located in unexpected places. One of the busiest sits inside a grey warehouse in an industrial estate five miles from London’s Heathrow airport. Here, every package sent by post from outside the UK weighing less than 2.2 kilograms meets Britain’s Border Force. More than two million parcels a day can be expected to travel through Royal Mail’s Heathrow Worldwide Distribution Centre, arriving straight from Britain’s ports, reflecting the British ability to be “very good e-shoppers”, according to Jon Thompson, chief executive of HM Revenue & Customs. Once inside the building, mail staff perform a triage. Any parcels suspected of…’